This invention relates generally to apparatus and methods for growing plants, and more specifically to controlled environment agriculture facilities and methods for plant cultivation in such facilities.
Controlled environment agriculture (CEA) is the cultivation of vegetable, ornamental and other plants in an enclosure within which those environmental factors which are generally recognized as influencing plant growth, maturation and productivity, are systematically time-programmed and carefully controlled. Typically the controlled growth factors include the intensity, duration and spectral distribution of illumination, the temperature, humidity and flow rate of the air, its carbon dioxide concentration, and the composition and temperature of the nutrient supplied to the growing plants. This latter parameter is most easily controlled in CEA installations in which hydroponics techniques are employed, as the nutrient solutions used with hydroponics may readily be analyzed for chemical composition and replenished as necessary to maintain their compositions within desired ranges of variation of the constituents.
A variant of the basic hydroponics technology which has been developing in parallel with CEA technology is the nutrient film technique developed by the Glasshouse Crop Research Institute, Littlehampton, England, and described in the following series of publications authored by Dr. A. J. Cooper of that institution:
"Improved Film Technique Speeds Growth", The Grower, Mar. 2, 1974. PA1 "Hardy Nursery Stock Production in Nutrient Film", The Grower, May 4, 1974. PA1 "Rapid Progress Through 1974 With Nutrient Film Trials", The Grower, Jan. 25, 1975. PA1 "Soil? Who Needs It?", American Vegetable Grower, Aug. & Sept., 1974.
Briefly, the nutrient film technique employs sloped tubes or troughs, commonly called gullies, in which the plant roots are contained and through which a continuous nutrient solution flow is effected. The quantity of nutrient flow is carefully controlled and normally held at a rate such that only a small part of the root mass is contacted by the nutrient stream directly, capillary attraction or "wicking" being relied on to extend the nutrient-wetted area over and through the entire root mass. Nutrient solution not absorbed by the plant roots is collected and recirculated, usually after analysis of its compositional elements and replenishment of any deficiency.
The combination of controlled environment agriculture and nutrient film techniques is a particularly synergistic one, with promise of extremely high yields of very high and consistent quality from even a relatively small facility. Other important advantages may also be realized. For example, the programmed control of plant environment affords immunity to weather variations and extremes, the potential for maintaining essentially sterile environmental conditions avoids problems of plant diseases and pests without need for the use of insecticides or fungicides, and the closed cycle supply of air and nutrients enables close to one hundred percent effective utilization both of the nutrient chemicals and of the water in which they are in solution. Research and development facilities for nutrient film CEA investigation have demonstrated conclusively the technical feasibility of this agricultural system, and have similarly shown its capability to produce extraordinary yields.
While technical feasibility has thus been conclusively and dramatically demonstrated, economic feasibility heretofore has presented a more difficult challenge. Among the factors significantly impacting CEA economics are the relatively high and increasing costs of electrical energy in many parts of the world, which are of significance because substantial amounts of electrical power are required both to provide the high intensity illumination necessary to maximize plant growth rates and to provide heating and cooling of the atmosphere within the facility.
Another factor affecting CEA economics derives from the requirement of growing plants that they be subject to alternate periods of illumination and relative darkness, this being necessary to provide the plants with regular periods of "rest" during which the illumination level is below the compensation point--the point at which the plant respiration just equals photosynthesis. Conventionally this requirement is met by switching the lighting system periodically on and off, and as a consequence the lights remain idle for substantial periods of time and are not fully utilized. Since the lighting systems currently preferred for controlled environment agriculture application are high intensity discharge (HID) lamps representing substantial capital investment, these periodic periods of idleness represent poor utilization of that investment, and the necessary repeated switching of the lamps on and off tends to reduce their total operating life.
This necessary on and off cycling of the lamps tends also to raise substantially both the initial cost and the cost of operation of the air temperature control means. The wide variations in heat output of the lamps when switched on and off often makes necessary a higher capacity air conditioning system, so as to provide adequate cooling when the full array of lamps is switched on, and it may also necessitate a higher capacity air heating system to provide adequate heating capacity when the lamp array is switched off in cold weather environments.
Another problem common in conventional controlled environment agriculture facilities results from non-uniformities in the supply of conditioned air to plants at all locations within the facility. In facilities in which space is efficiently utilized by relatively close concentration of plants, and particularly where the plant grow support racks are to be tiered to provide vertical distribution of plants as well as horizontal, it becomes very difficult to maintain uniformity of air distribution and air flow about all of the plants. With conventional air supply and distribution arrangements there normally will exist substantial inequalities of temperature and areas of stagnation of air, neither of which conditions is conducive to optimized plant growth. Air humidity control has also presented a problem, which commonly has been resolved by provision of precision humidity measurement equipment and automatically controlled fogging or other moisture addition equipment. These equipments tend to be expensive, both in initial costs and in maintenance.
Finally, conventional layouts of controlled environment agriculture facilities, in which access corridors are provided between each of the plant grow supports, are relatively inefficient in usage of the available floor space within the CEA enclosure. Such inefficiencies in space utilization tend to drive operating costs upwardly.
The present invention is directed towards a controlled environment agriculture facility, and methods for its operation, providing substantial improvements in the foregoing and other problem areas common in conventional CEA installations. CEA facilities in accordance with the invention afford optimized utilization of the energy input to the facility and correspondingly reduced electrical costs per unit yield from it. The invention also is directed to the provision of controlled environment agriculture facilities which afford good efficiency of utilization both of space within the facilities and of the personnel required to man them, and which afford ready adaptability to cultivation of different crops as desirable to meet seasonal and other changes in market conditions.
A controlled environment agriculture facility in accordance with the invention comprises an environmentally isolated enclosure within which is housed a plurality of plant grow support racks of rectangular configuration each provided with means enabling at least restricted movement of the rack along a line parallel to its width dimension. The plant grow support racks are arranged in a column formation, in contiguous or very closely spaced relation with each other. This arrangement achieves full utilization of the entire floor space of the CEA enclosure, save only a clear workspace area which may be located at either end of the enclosure and which is of width dimension somewhat greater than the width dimension of the plant grow support racks. Access to a desired individual plant grow support rack then may be accomplished at any time by shifting all the racks in the column between the rack to be accessed and the nearest adjacent end of the column, thereby freeing a space adjacent to that rack.
To provide the desired alternation of high level and low level illumination periods, an overhead lamp array is provided made up of a number and variety of lamps selected to provide the desired intensity and spectral distribution of illumination. The lamps of the array are arranged in groups with the groups spaced along a line parallel to the direction of movement of the plant grow support racks, with spacing between the center lines of adjacent lamp groups being made equal to an integral multiple of the spacing between centers of adjacent plant grow support racks. With this spacing, movement of all the plant grow support racks through a distance equal to half the distance or spacing between lamp groups will shift each support rack between a first position in which it is directly under one of the lamp groups, and fully illuminated thereby, and a second position in which it is located midway between lamp groups and so receives relatively low illumination. The necessary periods of reduced photosynthesis activity required for optimized plant growth are thus provided, while requiring substantially fewer lamps and permitting all the lamps to be operated continuously rather than cyclically. At the same time, the periodic shifting of the plant grow support racks between their illuminated and non-illuminated positions provides adequate opportunity to access each rack for performance of all needed operations on it.
The plant grow racks preferably are self-contained with each providing a number of plant grow containers or gullies extending the length of the rack. The plant root masses are contained within these gullies, and are supplied with nutrient through individual flow regulators. Nutrient distribution manifolding, overflow and return systems all are mounted to each rack in a manner to permit its free movement subject only to the limits imposed by the necessary nutrient supply and drain connections. These connections are made sufficiently flexible and extensible to enable shuttling of the racks between the fully illuminated and non-illuminated positions described above.
The CEA enclosure preferably is made as gas tight as possible so as to minimize escape of its contained atmosphere, the CO.sub.2 content of which may be enriched and controlled in conventional manner. The moisture or humidity content of the atmosphere also is controlled, and in accordance with the invention this is accomplished without requirement for an automatic humidity sensor and control system, simply by adjustment of means for variably bypassing the cooling coils of the air conditioning system so as to control the amount of water vapor removed thereby. It has been found possible in this way to maintain a balanced state between the amount of moisture added to the air through plant transpiration and the amount removed by the air conditioners, without need for fogging or other such water addition into the enclosure.
For optimized distribution of air and uniformity of air supply to and through each of the plant grow support structures, the air return system through which air is recirculated from the enclosure back to the air conditioning equipment includes a plurality of air flow control means. These control communication between the interior of the enclosure and the air return ducts, with at least one such control means being located in immediate association with each of the plant grow racks. This enhances equalization of the air flow to the individual racks and helps protect against stagnation of air adjacent to any of them. Alternatively, the air flow control means may be structurally integrated into the plant grow support racks, with rack movement then being permitted by flexible and extensible connections between the rack-carried air return structure and the fixed air return structure of the enclosure.
Substantial economies and improvements in efficiency, both technical and economic, result from the integrated configuration of plant grow support racks, arranged for mobility in the manner and to the extent described, with the lamp locations and spacings coordinated with support rack movement as described. This provides the desired capability for alternating periods of high level and low level illumination while permitting continuous operation of the lamps. At the same time, the control and equalization of distribution of conditioned air within the enclosure in the manner described minimizes temperature variations and areas of stagnation of the atmosphere, at all rack positions within the enclosure.
Typically, for example, with a CEA facility configuration having 50 percent of the floor area lighted continuously by overhead lamps and the plant grow support racks shifted between the full and low level illumination positions as herein described, only 30-60 percent as many lamps are required as would be the case if the lamps were switched on and off and covered the entire cropping area in conventional manner. Additionally, the resulting constancy of lamp heat output is beneficial for the reasons previously noted, and the lamps and their ballasts should offer longer life expectancies. These and the other cost efficiencies resulting from the use of controlled environment agriculture facilities in accordance with the invention substantially reduce the net cost per unit of product and enhance the economic viability of such facilities for large scale commercial application.